Aircraft have historically been equipped with a collection of mechanical or electro-mechanical flight instrument gauges that provide a pilot with information about the aircraft's position, orientation, speed, and performance. The gauges commonly provide quite limited breadth of functionality—typically only a single function. For example, the instrument panel of an aircraft employing such gauges might include an attitude indicator that shows the aircraft's orientation relative to the horizon, an altimeter that gives information about the aircraft's height above some reference level (e.g. sea-level) by measuring the local air pressure, an airspeed indicator that shows the aircraft's speed relative to the surrounding air, a heading indicator or magnetic compass that displays the direction the aircraft is pointing relative to north, or a turn and bank indicator that displays the direction of turn and rate of turn of the aircraft.
Integrated avionics systems replace mechanical and electro-mechanical instrument gauges with one or more electronic displays for displaying (e.g., presenting) primary flight information such as attitude, altitude, heading, vertical speed, and so forth, to the pilot. Integrated avionics systems may include one or more primary flight displays (PFD) and one or more multifunction displays (MFD). A representative PFD displays primary flight and selected navigation information that is typically received from one or more sensor systems such as an attitude heading reference system (AHRS), an inertial navigation system (INS), one or more air data computers (ADC) and/or navigation sensors. A representative MFD displays information for navigation and for broad situational awareness such as navigation routes, flight plans, information about aids to navigation (including airports), moving maps, weather information, terrain and obstacle information, traffic information, engine and other aircraft systems information, and so forth.